In the field of edge-type backlight module powered by LED, in order to make the backlight module slim and compact, the waveguide has become thinner and thinner. Currently, the thickness of the waveguide has reached to 2.00 mm. It is estimated that a waveguide of thickness of 1.5 mm or even 1.0 mm is expected in near future. According to the field requirements, the frame used to support and carries the waveguide will be distant to the waveguide in an area adjacent to the inlet of the light source. As a result, the waveguide will not be properly supported at the area adjacent to its inlet area. This arrangement will create a gap between the inlet of the waveguide and the frame. As the waveguide becomes thinner and thinner, the rigidity of the waveguide itself reduces as well. Accordingly, the waveguide tends to warp or bent easily. This warpage and bending will make the flareness of the waveguide become poor, creating an insufficient of illumination of the waveguide.